Laser oscillators or laser systems are used for various machining technologies such as fine laser machining, laser welding, laser marking and laser cutting. In particular, machining technologies such as a laser stepper, laser annealing, laser repair and laser dicing are exemplified as laser machining for semiconductors.
For example, Patent Document 1 discloses a manufacturing method for solar battery panels. According to the disclosure in Patent Document 1, laser annealing is used to manufacture the solar battery panels and crystallize non-crystalline silicon thin films. Accordingly, thin and light solar battery panels which efficiently generate electricity are inexpensively manufactured.
In general, various and strict manufacturing conditions are set for each of a series of steps for manufacturing semiconductors. Marks such as numbers, letters or barcodes are engraved in a dot format (dot marking) on a part of a semiconductor wafer surface in order to manage these manufacturing conditions for semiconductors.
In general, a semiconductor is manufactured through 100 or more steps. Processes for forming multiple elements and leveling the elements are carried out in each of the steps. These processes include various steps such as resist application, reduced projection of patterns onto the resist, and development of the resist, and leveling by various film formation steps (e.g., to form insulating films or metal films) to fill in gaps caused by copper wiring and the resist development.
FIG. 26 is a schematic view of a conventional laser beam machine for engraving marks in a dot format. The conventional laser beam machine is described with reference to FIG. 26.
The laser beam machine 900 in FIG. 26 irradiates continuous pulsed laser light onto a part of a surface of a semiconductor wafer WF to engrave marks in a dot format. The laser beam machine 900 includes a laser source 910, which emits laser light LB, and a scanning mirror 920, which reflects the laser light LB. The scanning mirror 920 reflects the laser light LB emitted from the laser source 910 towards the semiconductor wafer WF. Accordingly, the laser light LB is irradiated onto the semiconductor wafer WF.
FIG. 26 shows the X, Y and Z axes, which define a three-dimensional orthogonal coordinate system. The scanning mirror 920 rotates to move an irradiation position of the laser light LB in the Y axis direction.
The laser beam machine 900 also includes a stage 930 which supports the semiconductor wafer WF. The stage 930 moves the semiconductor wafer WF in the X axis direction. Accordingly, the irradiation position of the laser light LB on the semiconductor wafer WF is also moved in the X axis direction.
The laser source 910 oscillates pulses of the laser light LB. As a result of irradiating the laser light LB onto the semiconductor wafer WF at desired irradiation positions, a desired pattern is marked on a surface (hereinafter, called “work surface”) of the semiconductor wafer WF. In general, a solid laser source such as an Nd:YAG laser source or an Nd:YVO4 laser source is widely used as the laser source 910.
Patent Document 2 discloses technologies for reading out dot marks on a semiconductor wafer. According to the disclosure in Patent Document 2, a laser beam is irradiated from a He—Ne laser source onto a semiconductor wafer which is subjected to dot marking. Information indicated by the dot markings is read out on the basis of a reflectivity variation on the semiconductor wafer. Alternatively, a laser beam may be irradiated from a general laser source onto a semiconductor wafer which is subjected to dot markings. The information indicated by the dot markings may be read out on the basis of an oscillation variation of a heat wave caused by the laser beam.
Various manufacturing conditions are set for subsequent semiconductor manufacturing steps, on the basis of the read information from the dot markings. Unless the information in the dot markings is correctly read out (e.g., incorrect information is read from the dot markings), the semiconductor is handled as a defective product.
In many cases, reading errors in dot markings result from burred marks engraved by the aforementioned dot marking step. The burred marks may result from a form of the dots which constitute the marks. In general, a depth of the dots greatly affects clarity of the marks.
Patent Document 3 discloses technologies for obtaining dots of a prescribed height. According to the disclosure in Patent Document 3, a laser beam which has relatively high energy is irradiated once to melt and remove a part of a semiconductor in a spot shape so that a dot is formed. However, the disclosed technologies in Patent Document 3 may cause thick accumulation of molten materials after the melt and removal or scattered and deposited molten materials around the dot. Consequently, there may be a risk of impossible formation of elements, or elements may have worse quality.
Patent Document 4 discloses a laser marking method for engraving dots which have excellent visibility with little dust. According to the technologies disclosed in Patent Document 4, a swelled portion is formed at the center of a dot while a recess is formed around the swelled portion. Accordingly, the dot markings may achieve excellent visibility.
However, a conventional laser beam machine which carries out laser machining such as laser marking or laser annealing has various problems caused by a laser output variation of the laser source. Abrasion on a work-piece may result from the laser output of the laser source. The abrasion on the work-piece may result in dust as well as unclear markings. Consequently, processing errors may occur during subsequent processes.
Patent Document 1: JP 2008-112773 A
Patent Document 2: JP H2-299216 A
Patent Document 3: JP S60-37716 A
Patent Document 4: JP 2000-223382 A